Tap changers have existed in the art in numerous forms for many years. They usually comprise a selector and a load changeover switch.
The selector serves for power-free preselection of the new winding tap that is to be subsequently switched to.
The load changeover switch serves for the actual—rapid—uninterrupted changeover from the previous to the new winding tap preselected while not under load.
A tap changer with a selector is known from the company publication ‘OILTAP® M’ of the applicant, printing 03/09. In this selector, fixed selector contacts are arranged at an insulating-material frame circularly in a plurality of horizontal planes. These fixed selector contacts are connectable by a drive shaft that is centrally arranged in the interior of the insulating-material frame and that carries at least one movable selector contact in each horizontal plane of the fixed selector contacts. The fixed selector contacts, which are each in electrical connection with a respective winding tap of the associated tapped transformer that is to be regulated, are here thus arranged at and fastened to vertical insulating-material rods. These insulating-material rods can consist of resin-impregnated paper, glass-fiber-reinforced plastic or other insulating material. The insulating-material rods form a frame of vertical, mutually parallel rods; the frame is fixed by an upper ring and a lower ring.
A further tap changer is known from the company publication ‘VACUTAP® VV—Laststufenschalter für Regeltransformatoren’, printing 05/06, of the applicant. In the case of the selector shown there the fixed selector contacts are again arranged circularly in a plurality of horizontal planes and are connectable by a central drive shaft with movable selector contacts, but the arrangement of the fixed selector contacts is there provided in the wall of a closed insulating-material cylinder. Such an insulating-material cylinder can again consist of resin-impregnated paper, glass fiber-reinforced plastic or other insulating material.
Made known by the further company publication ‘VACUTAP®—Laststufenschalter für Ofenanwendungen’, printing 09/07, of the applicant is, inter alia, a tap changer of the type VR® in which the selector consists not of a closed insulating-material cylinder, but of a plurality of individual cylinder shells. These cylinder shells form individual segments that in the mounted state de facto form a cylinder contour with corresponding intermediate spaces.
A tap changer with a freewheel element is known from DE 10 2010 007 535 [US 2013/0213776]. The tap changer comprises a switching shaft to which a plurality of mutually parallel actuating elements is fastened. The actuating elements are constructed as cam discs with protrusions. Mechanical switching elements actuated by way of the protrusions of the cam discs are arranged parallel to the switching shaft. The mechanical switching elements are connected between the selector and the vacuum interrupters of the load changeover switch. Through actuation of the mechanical switching elements the vacuum interrupters in the load branch not conducting load current shall be protected from surge voltages that might arise.
A switch arrangement for a tap changer is known from DE 10 2010 020 137 A1. This tap changer, which serves for voltage-free or current-free switching between winding taps, comprises two integrally constructed fixing elements arranged one above the other in two planes. In addition, the fixing elements have, in the outer annular section, openings for the passage of contact rods. Moreover, each fixing element has a centrally arranged sleeve section in which a switching shaft is mounted. Two respective contact rods are electrically connected together and thus specific winding taps selected, by way of a contact arrangement fastened to the switching shaft.
A tap changer, which consists of a selector and a load switch, for transformers is known from U.S. Pat. No. 3,798,395. In that case the selector serves for power-free preselection of the winding tap and the load switch for rapid switching under voltage. The selector in that regard comprises two rotary contacts that connect each of the taps of the transformer with a respective collector ring and are in that case driven by way of a shaft.
A tap changer with a preselector for uninterrupted switching between different winding taps of a tapped transformer is known from EP 1 105 896 [U.S. Pat. No. 6,849,813]. Preselectors can in general be constructed on the one hand as a coarse tap selector and on the other hand as a reverser. In both cases the regulating range is by this means widened. In other words, multiple use can be made of existing selector contacts. The coarse tap selector realizes this in that a part of the main winding is switched on or switched off. It is possible by the reverser to add the regulating windings to the main winding or, however, to also connect these in opposite sense, thus subtract. A combination of coarse selector and reverser is also possible. As soon as a preselector is used, the actual selector is termed fine selector. In all three cases the preselector is arranged constructionally adjacent to the actual fine selector (selector). Here, too, the constructional realization takes place with the help of cylinder segments or a frame of insulating-material rods to which the movable and fixed preselector contacts are fastened.
The prior art with selectors of that kind for tap changers can thus be summarized as follows: The individual fixed selector contacts are arranged in several horizontal planes circularly around a rotatable drive shaft. The arrangement of the selector contacts and the fixing thereof takes place either at individual rods of insulating material, which form a cage frame, or in the wall of an insulating-material cylinder, or also in the wall of individual insulating-material cylinder segments that when joined together similarly form a circular arrangement.
As explained, the positioning of the fixed selector contacts vertically one above the other—in the case of an insulating-material frame, along the rods as carrier elements—takes place in a plurality of planes. Different subdivisions of the tap changer, i.e. the number of winding taps possibly to be connected and thus the number of fixed selector contacts, are realized by the different number of individual insulating-material rods, the diameter of the insulating-material cylinder or the different number of horizontal planes.
Widening of the regulating range is effected by way of preselectors constructed as coarse selectors, reversers or a combination of the two. These parts similarly consist of insulating-material cylinder segments or insulating-material rods that are arranged adjacent to the fine selector.
Overall, the prior art has various disadvantages. The principal disadvantage is that for different numbers of connectable winding taps of the associated tapped transformer and thus different numbers of fixed selector contacts different constructional forms of the selector are also required.
Due to the electrical voltage stability that has to be maintained the individual fixed selector contacts have to have a specific minimum spacing from one another not only horizontally, but also vertically. A large number of fixed selector contacts in a horizontal plane thus necessarily leads to a large diameter not only of the insulating-material frame, but also of the insulating-material cylinder. Equally, a large number of individual horizontal planes arranged one above the other leads to an increased length of both insulating-material frame and insulating-material cylinder.
In the case of extension of the fine selector (selector) by a preselector, such as, for example, a reverser, the diameter of the overall arrangement is substantially increased. It is also not possible to position this preselector below the fine selector in order to thereby usefully utilize construction space that may be available.
Thus, not only insulating-material rods and the respective fixing rings, but also different insulating-material cylinders in the most diverse dimensions have to be stocked by a manufacturer of tap changers; use of identical parts is thus extremely limited. Overall, this complexity leads to high costs.
Moreover, it is not possible in the production of tap changers to freely select whether a preselector in the form of a coarse selector or a reverser is arranged adjacent to or below the fine selector (selector).